//  ObjectiveComparator.java
//
//  Author:
//       Antonio J. Nebro <antonio@lcc.uma.es>
//       Juan J. Durillo <durillo@lcc.uma.es>
//
//  Copyright (c) 2011 Antonio J. Nebro, Juan J. Durillo
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU Lesser General Public License for more details.
// 
//  You should have received a copy of the GNU Lesser General Public License
//  along with this program.  If not, see <http://www.gnu.org/licenses/>.

package jmetal.util.comparators;

import jmetal.core.Solution;

import java.util.Comparator;

/**
 * This class implements a <code>Comparator</code> (a method for comparing
 * <code>Solution</code> objects) based on a objective values.
 */
public class ObjectiveComparator implements Comparator {

	/**
	 * Stores the index of the objective to compare
	 */
	private int nObj;
	private boolean ascendingOrder_;

	/**
	 * Constructor.
	 *
	 * @param nObj The index of the objective to compare
	 */
	public ObjectiveComparator(int nObj) {
		this.nObj = nObj;
		ascendingOrder_ = true;
	} // ObjectiveComparator

	public ObjectiveComparator(int nObj, boolean descendingOrder) {
		this.nObj = nObj;
		if (descendingOrder)
			ascendingOrder_ = false;
		else
			ascendingOrder_ = true;
	} // ObjectiveComparator

	/**
	 * Compares two solutions.
	 *
	 * @param o1 Object representing the first <code>Solution</code>.
	 * @param o2 Object representing the second <code>Solution</code>.
	 * @return -1, or 0, or 1 if o1 is less than, equal, or greater than o2,
	 *         respectively.
	 */
	public int compare(Object o1, Object o2) {
		if (o1 == null)
			return 1;
		else if (o2 == null)
			return -1;

		double objetive1 = ((Solution) o1).getObjective(this.nObj);
		double objetive2 = ((Solution) o2).getObjective(this.nObj);
		if (ascendingOrder_) {
			if (objetive1 < objetive2) {
				return -1;
			} else if (objetive1 > objetive2) {
				return 1;
			} else {
				return 0;
			}
		} else {
			if (objetive1 < objetive2) {
				return 1;
			} else if (objetive1 > objetive2) {
				return -1;
			} else {
				return 0;
			}
		}
	} // compare
} // ObjectiveComparator
